The present invention relates to rotary atomizers for atomizing coating materials, and in particular to an improved rotary atomizer which may be rapidly and completely cleaned of coating material.
Various types of rotary paint atomizers, which have means for cleaning the devices of one color of paint in preparation for atomizing paint of another color, are known in the art. For example, the atomizer taught by U.S. Pat. No. 4,275,838 is surrounded by a shroud mounted for movement around and coaxial to the atomizer. During a painting operation, the shroud is retracted to a position allowing paint to be projected from the edge of the atomizer. Upon completion of the painting operation, incident to a change in color of coating material to be atomized, the shroud is moved forwardly to a point whereat it surrounds the atomizer. A flushing nozzle in the shroud faces toward the paint feed surface at about the axis of the atomizer when the shroud is in its forward position, and a stream of flushing media is directed onto the surface at about the axis to rinse any paint residue from the surface. Upon completion of flushing, the shroud is moved rearwardly to its position away from the atomizing edge of the device and paint of a new color is supplied to the device. Although the arrangement cleans the atomizer, simpler flushing systems are available which avoid use of a separate flushing nozzle carried in a reciprocable shroud.
One such cleaning system is disclosed by U.S. Pat. No. 4,405,086 to Vetter, in which paint is delivered through a passage extending coaxial to the axis of rotation of the atomizer, into a rearward paint cup of the device. A passageway extends between the paint cup and a forward paint feed surface of the atomizer from an edge of which paint is projected, and the passageway both begins in the paint feed cup and terminates on the paint feed surface along the axis of the atomizer. Paint is introduced into the paint cup through a nozzle coaxially aligned with the inlet to the passageway, and to prevent paint from squirting out of the end of the passageway and beyond the paint feed surface, the passageway follows a labyrinth path between the paint cup and paint feed surface, first diverging radially outwardly and then radially inwardly. However, to provide the labyrinth path requires tapping a plurality of angulated passages through a center hub on the rearward side of the wall between the paint feed cup and paint feed surface, which adds complexity and cost to the manufacture of the device. At the same time, because paint introduced into the cup is directed in a jet against the inlet to the passageway, there is an increased pressure of paint in the passageway, in consequence of which paint has a tendency to be projected beyond the paint feed surface as it exists the passageway.
Another rotary atomizer which may be cleaned without use of a separate flushing nozzle in a shroud is taught by U.S. Pat. No. 4,505,430 to Rodgers et al. In that atomizer, a plurality of passageways extend between a rearward paint cup and a forward paint feed surface of the device, from an edge of which surface atomization occurs. The passageways initiate in the paint cup at a first non-zero radius and terminate on the paint feed surface at a second and smaller non-zero radius radially inwardly from the first radius. The passageways are angled both in the radial direction and tangentially, such that the tangential inclination is in a direction opposite the direction of rotation of the atomizer. Two separate nozzles extend into the paint cup, one for paint and one for cleaning solution, and during cleaning of the atomizer the nozzle for cleaning solution forcefully directs the solution into inner ends of the passageways as they rotate past the nozzle. One disadvantage of the device is that because the passageways terminate on the paint feed surface at a nonzero radius outwardly from the axis of rotation, the very center of the surface is not cleaned of paint residue. Also, the large number of passageways required and their particular angulation add cost to the manufacture of the device.